Alarm device

ABSTRACT

This invention relates to a monitoring device comprising a generator for generating longitudinal compressive waves of ultrasonic frequency and a receiver unit for monitoring the amplitude of the waves at the ultrasonic frequency received by a receiver. The receiver unit includes an oscillator for generating a signal train at a given carrier frequency and first switch means for controlling the transmission of the signal train at that carrier frequency to a remote detector unit, said first switch means being actuated in response to a change in the amplitude of the signal received by the receiver. The detector unit is tuned to the carrier frequency and has a further switch means under the control of the signal train (preferably transmitted via the power lines wiring) for actuating an alarm and/or recording device to indicate when the amplitude of waves received by the receiver has changed.

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llnited States Patent Everitt Apr. 25, 1972 1 ALARM DEVICE 2,071,9332/1937 Miessner ..340/258 [721 Kenneth John London, England 311353322332 i2%?.1i3333.......... 31313535332 [73] Assignee: Donald PatrickWhite, Loughton, Essex, 3,378,829 8 Alati 8! a "3 16 Englanda partinterest Bagno [22] Wed: Sept 1969 Primary ExaminerDavid L. Trafton 2 1p NO: 860,240 Attorney-Curtis, MOlliS & Safford [57] ABSTRACT [30]Forelgn Apphcanon pnomy Dam This invention relates to a monitoringdevice comprising a Sept. 26, 1968 Great Britain ..45,782/68 generatorfor generating longitudinal compressive waves of ultrasonic frequencyand a receiver unit for monitoring the am- [52] US. Cl ..340/4l6,325/474, 340/216, plitude of the waves at the ultrasonic frequencyreceived by a 340/258 B, 340/276 receiver. The receiver unit includes anoscillator for generat- [51] Int. Cl. ..G08b 13/16 ng a signal train ata given carrier frequency and first switch 53 Field f Search gm/27310353153 153 13 means for controlling the transmission of the signaltrain at 340 21 41 325/474 that carrier frequency to a remote detectorunit, said first switch means being actuated in response to a change inthe 56] References Cited amplitude of the signal received by thereceiver. The detector unit is tuned to the carrier frequency and has afurther switch UNITED STATES PATENTS means under the control of thesignal train (preferably transmitted via the power lines wiring) foractuating an alarm 3,135951 6/1964 BYYPe ""340/276 and/or recordingdevice to indicate when the amplitude of 3,287,722 1 H1966 Craig....340/3l0 waves received by the receiver has changed. 3,513,463 5/1970Stevenson, Jr. et al.. ....340/258 3,388,389 l/l968 Henriques ..340/3l08 Claims, 3 Drawing Figures I43, l n J- I I W I H t '1 AZ 16 m D 2 iPATENTEDAPR 25 1912 SHEET 10F 3 Q II I1 I! 1| ..|||l|||| I l I l I I Il| !l|. l i i I III. M I, II I II M r 1 5 MN 5 I RM is H H ANN w v h aas *5 I l Q a5 w w I I I I l I I [1W1]! llllil.

ALARM DEVICE This invention relates to a monitoring device for detectingmovement of an object and in particular, but not exclusively, to adevice for detecting the presence of an intruder in an enclosure.

Enclosure monitoring devices (e.g. burglar alarms) are known in whichultrasonic waves are employed in the enclosure and the device senseschanges in the frequency of reflected waves to indicate the presence ofa moving object in the enclosure (the well known Doppler effect willcause an increase or decrease in the frequency of the wave reflected offa moving object depending on whether that object is moving towards thesource or away from the source). Such prior art devices require to behighly stabilised if they are to give a reliable indication of the entryof an intruder into the enclosure and further must be highly sensitiveas to frequency changes if they are to respond to slow moving objects,but not to respond to drift which may occur in the output frequency ofthe wave generator.

A device in accordance with the present invention relies on detectingchanges in the amplitude of reflected waves and can thus be designedwithout regard to close coupling between the generator and the receiver.

In many cases it is desirable that the vicinity where an alarm israised, in the event of undesirable entry into the enclosure, is remotefrom the enclosure being protected. For example, it may be desirable forthe alarm to be raised in a nightwatchmans room at a factory orwarehouse which may be many metres (even several hundred metres) awayfrom the protected enclosure. With prior art devices it is necessary tocouple a part of the device in the protected enclosure with a furtherpart in the vicinity where the alarm is to be raised by means ofspecially laid wires and this increases the cost of the installation ofthe device and the susceptability of the device to failure and/ortampering by would-be intruders.

One important feature of the present invention is that the constructionof the device enables the wiring of conventional power lines to be usedas the link between the two parts of the device.

A further important feature of the present invention is that it can beused in unenclosed areas (e.g. open-air storage dumps or aerodromes) andcan detect the presence of an intruder in the area many metres from thedevice by monitoring the appearance of reflected waves from theintruder.

According to the invention a monitoring device comprises a generator forgenerating longitudinal compressive waves of ultrasonic frequency, areceiver unit for monitoring the amplitude of the waves at theultrasonic frequency received by a receiver, an oscillator forgenerating a signal train at a given carrier frequency, first switchmeans for controlling the transmission of the signal train at thatcarrier frequency to a detector unit, said first switch means beingactuated in response to a change in the amplitude of the signal receivedby the receiver, the detector unit being tuned to the carrier frequencyand havin g a further switch means under the control of the signal trainfor actuating an alarm and/or recording device to indicate when theamplitude of waves received by the receiver has changed.

In a preferred embodiment of device in accordance with the invention thesignal train is at a frequency of many kilocycles and is transmitted tothe detector unit via the power lines. Conveniently the generator andthe receiver are housed in one cabinet deriving its power supply from apower line outlet and feeding the signal train to that power line outletand the detector unit (which may or may not include the alarm and/orrecording device) is connected to a power line outlet at a positionremote from the generator/receiver unit.

The generator and receiver may be a matched pair of piezoelectricdevices and conveniently operate at a frequency greater than 22kilocycles and preferably greater than 30 kilocycles. 40 kilocycles hasbeen found to be a suitable operating frequency.

Since the detector is sensitive to changes in the signal train passed toit (e.g. via the power lines) from the generator/receiver unit it mayrespond to a change in frequency of the signal train, the appearance ofthe signal train or the disappearance of the signal train. Thus, forexample the oscillator may be working all the time but its output isonly switched to the detector (or its output is only switched off fromthe detector) when there is a change in the wave pattern received by thereceiver. Alternatively, the oscillator can be made to oscillate (or putout of oscillation or made to oscillate at a different frequency towhich the detector is insensitive) when there is a change in the wavepattern received by the receiver.

Where a plurality of generator/receiver units are to be em ployed in aplurality of different locations (e.g. around the perimeter of an openspace or in a plurality of different enclosures) and the presence of anintruder in the vicinity of any generator/receiver is required to beindicated in a single detector unit, all the generator/receiver unitsmay employ generators operating at the same frequency but with thesignal train from each generator/receiver unit being modulated at adifferent frequency. The single detector unit can then be provided withan input channel for each generator/receiver unit each channel beingresponsive to a different one of the modulated signal trains.

Conveniently, to minimize spurious actuation of the device, actuation ofthe first switch means only occurs following a change in amplitude ofthe signal received by the receiver which is greater than a presetminimum or occurs for a time period greater than a preset minimum time.

One embodiment of enclosure protection device in accordance with theinvention will now be described, by way of example with reference to theaccompanying schematic drawings.

FIG. 1 shows a burglar alarm which comprises a generator/receiver unitshown within the dotted line 1 and a detector unit shown within thedotted line 2, the generator/receiver unit 1 being located within anenclosure in which the presence of intruders is to be detected and thedetector unit 2 being located at any position remote from the enclosure,the connection between the two units being via the power supply (shownas the dotted link 3).

The generator/receiver unit comprises a highly stabilized power pack 4,feeding an oscillator 5 which in turn is supplying HF power to a sonicemitter 6.

The power pack 4 conveniently comprises a full-wave rectifier with anassociated smoothing circuit and a transistor- Zener diode bridging pathto maintain a stabilised DC output irrespective of wide fluctuations ofAC input. The oscillator 5 is conveniently transistorised and operatesat approximately 40,000 cycles per second. The sonic emitter 6 isconveniently a piezoelectric crystal. The combination of integers 4, 5and 6 gives rise to the emission of longitudinal compression waves fromthe emitter 6 at ultrasonic frequencies, the waves generating a standingwave pattern in the enclosure in which the unit 1 is placed.

A further piezoelectric crystal is employed as a receiver 7 and this isplaced close to the emitter 6 to monitor reflected waves reaching itfrom reflecting surfaces in the enclosure. An amplifier 8 (tuned to thefrequency of the ultrasonic waves) amplifies the output of the receiver7 and feeds it to an amplitude level detector 9. In a preferredembodiment, the integer 9 comprises an envelope detector which senseschanges in the output of the amplifier 8. The envelope detector maysimply be a capacitor connected to receive the half-wave rectifiedoutput of the amplifier 8, any change in the charge stored by thecapacitor signifying a change in the amplitude of the waves reaching thereceiver 7. The amplifier 10 serves as an envelope amplifier andamplifies the output signal of the amplitude level detector 9 so that itis sufiicient to actuate any convenient switch means 11 and thus controlthe operation of a signal oscillator 12. In one embodiment, theoscillator 12 is working continuously and the switch means, e.g. atransistor or a solenoid reed switch) on actuation merely serves to feedthe oscillator output into the power 3 or to disconnect the oscillatorfrom the power 3. Alternatively, the switch means 11 may be employed toturn the oscillator on or off, the oscillator output being connected tothe power lines 3 throughout. If the arrangement is such that, underconditions of a uniform amplitude of reflected waves (i.e. a stationarystanding wave pattern), the oscillator is connected to the power lines3, there is the advantage that any disconnection of thegenerator/receiver unit 1 is instantly detected and thus makes thedevice less susceptible to being rendered inoperative by an intruder.

The frequency of the oscillator can be chosen to be any convenient valuebearing in mind that it is required to generate a signal train fortransmission through the power system. One convenient frequency for thispurpose has been found to be 120 kilocycles. Frequencies in the range100 to 260 kilocycles can also be employed.

The detector unit 2 has its own power supply 13, an amplifier 14 tunedto the frequency of the oscillator 12 a switch means and any convenientalarm or count recorder 16. The amplifier 14 actuates the switch means15 when the signal train from the oscillator 12 either appears on thepower lines 3 or disappears from the power lines 3 depending on the modeof operation selected. In either case, the alarm or count recorder 16 isactuated.

The emitter 6 and the receiver 7 may be located side by side in the samecabinet and it is then merely necessary to place that cabinet in theenclosure and to connect the generator/receiver unit to the power lines.The detector unit is then plugged into the power lines at some otherpoint (and in practice it has been found possible for the receiver to beseveral hundred metres away from the detector) to obtain an indicationwhenever the standing wave pattern in the enclosure is disturbed.Alternatively, the emitter 6 and the receiver 7 may be spatiallyseparated in which case the standing wave pattern between them ismonitored and in this way a larger enclosure can be protected. Thearrangement in which the oscillator 12 is normally quiescent and onlyoscillates when there is a change in the standing wave pattern has theadvantage that a plurality of generator/receiver units, each with itsown oscillator 12 tuned to the same frequency, can be coupled to asingle detector unit to monitor a plurality of separated enclosures, adisturbance of the standing wave pattern in any of the enclosures beingdetected on the detector unit. With this modified arrangement, however,the circuit in the detector unit has to be adapted to distinguishbetween a signal derived from an oscillator 12 and a spuriousoscillation on the power lines at the frequency of the oscillator butnot associated with any of the oscillators. One way of achieving thisdistinction is to provide the detector unit 2 with two amplifiers 14 onetuned to accept signals at the oscillator frequency and the otherfiltered to accept any frequency except the oscillator frequency and toarrange for the switch 15 to be actuated only when a signal is passed toit from the one amplifier but not from the other amplifier.

An alternative method of distinguishing between a true signaltransmitted from an oscillator at the predetermined frequency and noise"(which will be of broad-band character) is to employ two tunedamplifiers connected in parallel, one tuned to the predeterminedfrequency of the oscillator and the other tuned to a different frequencysuitably spaced from the predetermined frequency, (For example, if theoscillators are tuned to transmit signal trains at 120 kilocycles oneamplifier in the detector unit would be tuned to 120 kilocycles and theother tuned to (say) 390 kilocycles). The outputs from the two tunedamplifiers are led to a discriminating switch unit which actuates thealarm only on the appearance of an output from the one amplifier and noton the appearance of outputs from both amplifiers or the appearance of asignal just from the other amplifier.

Although the primary purpose of the device is to protect an enclosureagainst intruders it will be appreciated that since the device isactuated whenever there is a change in the wave pattern as monitored bythe receiver 7, the device can be used for other applications, forexample for counting the number of people passing into a building (inthis case each disturbance of the standing wave pattern caused by aperson passing into the building is used to actuate a count recorderrather than an alarm) or on the occasion of a fire in the enclosurewhich will give rise to energetic air currents sufficient to change theamplitude of waves received by the receiver 7.

FIGS. 2 and 3 of the drawings show typical circuits for a device inaccordance with the invention.

FIG. 2 shows the circuits for integers 7 to 12 of FIG. 1 (integers 4 to6 are wholly conventional and need not be further described) and FIG. 3shows a typical detector unit 2 having two tuned amplifiers 14a and 14bfor discriminating between a genuine signal and noise on the powerlines.

Referring to FIG. 2 the output from the receiver 7 is fed to a two-stagetuned amplifier (amplifier 8) via an emitter-follower circuit. Acapacitor C, serves as the amplitude level detector 9 which is followedby a two-stage envelope" amplifier 10. The output from this amplifier isled to a Darlington pair D via a leakage path (a resistor R and acapacitor C whose impedance is adjustable to control the sensitivity ofthe device so that alarm only arises following a signal from theamplifier 10 which is greater than a preset minimum signal and occursfor a time longer than a preset minimum time.

A relay A, forms the final stage of the switch means 11 and actuates anoscillator 12 connected to the link 3 in either of two ways. Theconnections shown in FIG. 2, are for positive signalling" in which casethe oscillator 12 only oscillates when the relay A closes (thustransmitting the signal train only when alarm conditions occur). Ifhowever, the contact YY is made (rather than the contact YY as shown)and the contact XX is also made the arrangement for negative signalling"is obtained and the oscillator will normally oscillate but will becomequiescent on the closing of the relay A,.

The upper amplifier (14a) in FIG. 3 is tuned to the frequency of theoscillator 12 while the lower amplifier (14b) is tuned to a differentfrequency in the noise band. If the positive signalling mode is employedboth amplifiers will be required the circuit being arranged so that theDarlington pair D only energises a relay A if a signal is received fromthe amplifier 14a without a signal from the amplifier 14b. If thenegative signalling mode is employed, the amplifier 14b is not requiredbut the diode D is reversed and a resistor R (shown dotted) is employedin the position shown.

If the amplifier 14b is omitted it is desirable to retain the Zenerdiode and parallel connected capacitor (shown on the right of amplifier14b) in the circuit of amplifier 14a, since these components have asmoothing and stabilising effect on the HT lines of both amplifiers.

The power pack 13 has not been shown in FIG. 3 since this can be of anyconventional design.

I claim:

1. A monitoring device comprising a generator,

a receiver and a detector unit, the generator having an emitter forgenerating longitudinal compressive waves of ultrasonic frequency thereceiver having means for receiving longitudinal compressive waves atsaid frequency, means for monitoring the amplitude of the waves receivedby said receiving means, an oscillator for generating a signal train ata given carrier frequency, a power line connection cord and first switchmeans for controlling the transmission of the signal train at saidcarrier frequency to the power line connection cord in response to achange in the amplitude of the signal received by said receiving meansthe detector unit having a further power line connection cord, anamplifier tuned to said carrier frequency, a further switch meanscontrolled by the amplifier and indicating means controlled by thefurther switch means whereby the indicating means is under control ofthe signal train and indicates when the amplitude of waves received bysaid receiving means in the receiver has changed; said detector unitfurther including a second tuned amplifier only one of the twoamplifiers being tuned to receive the signal train, said further switchmeans including discriminating means which actuates the indicating meansonly when an output is received solely from said one amplifier tuned toreceive the signal train.

2. A monitoring device as claimed in claim 1, in which the generator andthe receiver are proximately housed having a single power lineconnection cord which serves both to supply electric power to thegenerator and receiver from a power line and for impressing the outputof the oscillator on the power line, said further connection cord of thedetector unit serving to supply electric power to the detector unit andto transmit the signal train impressed on the power line to said tunedamplifier.

3. A monitoring device as claimed in claim 1, in which said first switchmeans in said receiver stops the transmission of a signal train to thedetector unit when the amplitude of the waves received by said receivingmeans changes by more than a predetermined amount in less than apredetermined time.

4. A monitoring device as claimed in claim 2, in which said first switchmeans in said receiver'stops the output of said oscillator from reachingsaid connection cords when the amplitude of the waves received by saidreceiving means changes by more than a predetermined amount in less thana predetermined time. 7

5. A monitoring device as claimed in claim 1, in which the oscillator insaid receiver only impresses a signal train on said power lineconnection cords when the amplitude of the waves received by saidreceiving means changes by more than a predetermined amount in less thana predetermined time.

6. A monitoring device as claimed in claim 2, in which the receiveroscillator only impresses a signal train on the power line connectioncords when there is a change in the wave pattern received by saidreceiving means in said receiver.

7. A monitoring device as claimed in claim 1, in which said emittergenerates waves at a frequency greater than 30 kilol-Iertz.

8. A monitoring device as claimed in claim 1, in which said emittergenerates waves at a frequency greater than 30 kilol-lertz.

1. A monitoring device comprising a generator, a receiver and a detectorunit, the generator having an emitter for generating longitudinalcompressive waves of ultrasonic frequency the receiver having means forreceiving longitudinal compressive waves at said frequency, means formonitoring the amplitude of the waves received by said receiving means,an oscillator for generating a signal train at a given carrierfrequency, a power line connection cord and first switch means forcontrolling the transmission of the signal train at said carrierfrequency to the power line connection cord in response to a change inthe amplitude of the signal received by said receiving means thedetector unit having a further power line connection cord, an amplifiertuned to said carrier frequency, a further switch means controlled bythe amplifier and indicating means controlled by the further switchmeans whereby the indicating means is under control of the signal trainand indicates when the amplitude of waves received by said receivingmeans in the receiver has changed; said detector unit further includinga second tuned amplifier only one of the two amplifiers being tuned toreceive the signal train, said further switch means includingdiscriminating means which actuates the indicating means only when anoutput is received solely from said one amplifier tuned to receive thesignal train.
 2. A monitoring device as claimed in claim 1, in which thegenerator and the receiver are proximately housed having a single powerline connection cord which serves both to supply electric power to thegenerator and receiver from a power line and for impressing the outputof the oscillator on the power line, said further connection cord of thedetector unit serving to supply electric power to the detector unit andto transmit the signal train impressed on the power line to said tunedamplifier.
 3. A monitoring device as claimed in claim 1, in which saidfirst switch means in said receiver stops the transmission of a signaltrain to the detector unit when the amplitude of the waves received bysaid receiving means changes by more than a predetermined amount in lessthan a predetermined time.
 4. A monitoring device as claimed in claim 2,in which said first switch means in said receiver stops the output ofsaid oscillator from reaching said connection cords when the amPlitudeof the waves received by said receiving means changes by more than apredetermined amount in less than a predetermined time.
 5. A monitoringdevice as claimed in claim 1, in which the oscillator in said receiveronly impresses a signal train on said power line connection cords whenthe amplitude of the waves received by said receiving means changes bymore than a predetermined amount in less than a predetermined time.
 6. Amonitoring device as claimed in claim 2, in which the receiveroscillator only impresses a signal train on the power line connectioncords when there is a change in the wave pattern received by saidreceiving means in said receiver.
 7. A monitoring device as claimed inclaim 1, in which said emitter generates waves at a frequency greaterthan 30 kiloHertz.
 8. A monitoring device as claimed in claim 1, inwhich said emitter generates waves at a frequency greater than 30kiloHertz.